Question

How does the fish circulatory system differ from the mammal circulatory system? (Be comprehensive.) Name one significant feature that is the same between fish and mammal circulation.

Answer 1

n mammals (like us) there is a double circulation. The right side of the heart receives blood returning back from the body; this blood is low in Oxygen. This “deoxygenated” blood enters the right atrium and then the right ventricle to be pumped to the lungs were the blood will be oxygenated. The oxygenated blood from the lungs enters the left ventricle via the left atrium and is then pumped out into the larger body circulation. Note that the volume pumped by the right and left side of the heart is the same: approximately 5 liters per minute in a 70 kg human.

In fish, the heart only has one atrium and one ventricle. The oxygen-depleted blood that returns from the body enters the atrium, and then the ventricle, and is then pumped out to the gills where the blood is oxygenated, and then it continues through the rest of the body.

the major difference between the mammalian and fish circulatory system. The fish heart needs to generate the driving pressure for both the gills (lungs in mammals) and the body since they are connected in series,

In mammals both sides of the heart pump the same volume per time unit, but the pressure generation is very different in the right and left side. The right ventricle only generates a fraction of the pressure compared to the left ventricle (which is the pressure you measure during a physical exam. This pressure should normally be around 120/80 mmHg. To optimize the gas exchange in the lungs, the diffusion distance needs to me minimized. A small diffusion distance means thin membranes, and this means that the blood pressure in the lung circulation should be low in order to avoid damage. In fish, the heart pumps blood first to the gills where the gas exchange takes places, and then the blood continues to the rest of the body. This is a fine balance, since the fish's gills (like the mammal's lungs) have to be thin walled to facilitate gas exchange ,and thus cannot tolerate high blood pressure. At the same time, the blood pressure will drop when the blood cells squeeze through the lamellae (see the respiration module), and the blood pressure that remains after the blood had passed through the gills has to be high enough to drive the blood around the body.

A similarity between the circulatory system of a fish vs. the circulatory system of humans are the gills and the lungs. Although they are very different from a purely physical standpoint, they both function in pulling oxygen from the surrounding water or air and putting it into their bloodstream